So how important is neck tension?

[South Pender]

I'm in the process of working up loads for my Sako sporter 6 PPC and have tried two powders (H322 and VV 133) and two bullets (Bart's and Watson 68-gr.) now, and have varied seating depth and powder-charge weight in my quest for best accuracy. With all these factors being varied, there are a lot of variables--and resulting combinations--at work in the process. I'm loathe to add still another variable--neck tension--but am wondering whether perhaps I should. All of my loads so far (with by now about 150 rounds down the tube) have been with .002" neck tension (if that's how we measure it)--by which I mean I have sized the necks down (with a Wilson chamber-type neck-sizer) to .002" less than the OD of the loaded rounds' necks. More specifically, I've used the .260" bushing for the OD of loaded necks of .262".

So here's my question. Can I realistically expect any change in performance (group size) by trying some loads with .003" neck tension--i.e., using the .259" bushing for the OD of loaded necks of .262"? Adding still another variable into the process adds to the complexity of the load-development process, but if there's some chance that different results may be expected by varying neck tension, I guess I should try this. I've read that certain powders work better with greater neck tension than do some other powders. Is there enough here to try this, or am I likely to see no change in performance?

 

[Sniper338]

Neck tension is HUGE...

 

[joshb]

Ditto.......and add seating depth!

 

[Tim Singleton]

.002 is a good place to be for the PPC some do use more.

How are you doing you seating depth and load testing?
I don't think you will tell any difference in your rifle by changing neck tension. A full blown bench rifle maybe

 

[243winxb]

Measure the sized neck with a micrometer, before and after seating a bullet. It should expand about .002" for my preferred neck tension.

 

[mikecr]

I mean I have sized the necks down (with a Wilson chamber-type neck-sizer) to .002" less than the OD of the loaded rounds' necks. More specifically, I've used the .260" bushing for the OD of loaded necks of .262".

Does this mean you actually measure 2thou smaller neck OD from loaded?

Can I realistically expect any change in performance (group size) by trying some loads with .003" neck tension--i.e., using the .259" bushing for the OD of loaded necks of .262"?

If seated bullet bearing is below length of neck sized, then going lower with interference fit wouldn't do anything to tension. A seating bullet just expands it right back out, and spring back gripping the bearing is no more than ~1thou anyway. It holds in this scenario even if you sized down 10thou interference fit.
So I doubt a smaller bushing in your Wilson would do anything for you.

 

[savagedasher]

We have the best ppc shooters in the world they should give you the answers Larry

 

[Richard Coody]

I'm in the process of working up loads for my Sako sporter 6 PPC and have tried two powders (H322 and VV 133) and two bullets (Bart's and Watson 68-gr.) now, and have varied seating depth and powder-charge weight in my quest for best accuracy. With all these factors being varied, there are a lot of variables--and resulting combinations--at work in the process. I'm loathe to add still another variable--neck tension--but am wondering whether perhaps I should. All of my loads so far (with by now about 150 rounds down the tube) have been with .002" neck tension (if that's how we measure it)--by which I mean I have sized the necks down (with a Wilson chamber-type neck-sizer) to .002" less than the OD of the loaded rounds' necks. More specifically, I've used the .260" bushing for the OD of loaded necks of .262".

So here's my question. Can I realistically expect any change in performance (group size) by trying some loads with .003" neck tension--i.e., using the .259" bushing for the OD of loaded necks of .262"? Adding still another variable into the process adds to the complexity of the load-development process, but if there's some chance that different results may be expected by varying neck tension, I guess I should try this. I've read that certain powders work better with greater neck tension than do some other powders. Is there enough here to try this, or am I likely to see no change in performance?

what is you chamber neck diameter?

are you neck turning your brass?

the outside diameter of the neck brass of a loaded round is .262?

what is the diameter of the neck of a fired case?

 

[ShootDots]

Many PPC shooters use very thin neck walls. Nine (9) thousandths neck wall thickness at least used to be "the standard". I never shot a PPC, however, I shot with quite a few "Benchresters" 30+ years ago who did. Most, if not all had very "thin" neck walls on those cases. With neck walls that thin, they had to run heavier neck tensions to properly hold the bullets. Three to four thousandths, if memory serves me correctly, is what most used. If you have thicker necks, basically from "skim turning" the necks, my bet would be from about 1/2 to 2 thousandths TOPS will get you better accuracy than the 3-4 they used to use with the thin necks.
If we have some OLD HEAD Benchresters here who shoot the PPC, they will chime in and give you GOOD info..

 

[msinc]

I will say this about neck tension...it can be confusing to say the least. I would suggest you do all the other work up stuff on all the other variables and make worrying about neck tension last on the list. What I have seen with neck tension is that you can have pretty decent groups with the SD/ES numbers not looking too great. Back off the neck tension and get them consistent and see the SD/ES numbers look fantastic, only to have groups open up or best case not get any better at all.

 

[alb]

OP, what's your intended purpose for the ammunition?

 

[skiutah02]

In my experience with certain caliber/bullet combos (not 6ppc however), neck tension has proved to be a more critical accuracy variable than powder or seating depth. I have halved my vertical at 300yds with a 0.001 change in bushing size. Neck tension consistency has been extremely important to accuracy in across every caliber I have tested with perhaps one exception (140H in 6.5x47L). Drew

 

[Richard Coody]

Many PPC shooters use very thin neck walls. Nine (9) thousandths neck wall thickness at least used to be "the standard". I never shot a PPC, however, I shot with quite a few "Benchresters" 30+ years ago who did. Most, if not all had very "thin" neck walls on those cases. With neck walls that thin, they had to run heavier neck tensions to properly hold the bullets. Three to four thousandths, if memory serves me correctly, is what most used. If you have thicker necks, basically from "skim turning" the necks, my bet would be from about 1/2 to 2 thousandths TOPS will get you better accuracy than the 3-4 they used to use with the thin necks.
If we have some OLD HEAD Benchresters here who shoot the PPC, they will chime in and give you GOOD info..

that is exactly why i am asking these questions.

if his loaded round is .262 then he has to be turning that brass. it would be closer to .270 if he wasn't. you are right those thin walled.cases.can like.a lot of neck tension. have to let the rifle tell you what it likes.

he said.a.sportster 6PPC. the varmint guys are using unturned brass with chambers.i the .272 to .275 range. that is why i asked about the fired.brass diameter.

 

[tuttlefarm]

Consistent neck tension is very important. In short range seating depth is next then powder charge.

 

[Toby Bradshaw]

I'm loathe to add still another variable--neck tension--but am wondering whether perhaps I should. ... Is there enough here to try this, or am I likely to see no change in performance?

But whether you can see any difference depends on you and your rifle. With a full-blown benchrest rifle and a proficient shooter, neck tension matters.

 

[joshb]

I reread your post. I'll say this: You are not adding another variable. It's there, wether you are aware of it or not. Understanding it's affect on your accuracy is important. It falls into "careful what you wish for", though. Seeking knowledge can kick your ass. Learning what the important variables are is just the first step. Finding what your gun "likes" by testing all the variables can turn into a LOT of work. Keep good records! In the end, it is very rewarding when you finally nail it down and get tiny groups out of your gun. I might be a little addicted to this fun process, like a lot of guys, here. I've done load work up for quite a few guns and I keep buying and building more. I figure it will take me a couple years of shooting to deal with what I already have finished and I'm building a couple more.

 

[snert]

Sako Sporter...

So theoretically neck tension matters a lot. But not as much when the firearm being used lacks the ability to show that difference. We are talking about a sporter off a rest here. Ok, yes, it is a good one, but neck tension is likely NOT going to be definable (is that a word) using a sporter. How the heck is he gonna know if it is bench manners, wind, barrel heating, a factory barrel, rest design, stock design...that keeps him out of the 2's? The OP should use good brass, observe proper techniques, be consistent and fiddle with seating depths. If he gets good enough to shoot in the 2's all the time with that sporter then we need to start talking neck tension testing. Till then, it is chasing an ethereal number, a phantom that cannot be defined or caught. Just my opinion.

 

[South Pender]

Many thanks to all of you who have chipped in with valuable insights. Just to answer some questions, I don't know the chamber neck diameter (I haven't made a chamber cast), but I suspect it is in the .270"-.272" range. This is the typical Sako 6 PPC-USA chamber, so nothing like the earlier custom .262" chambers.

Yes, I am neck-turning, and have turned the necks to about .0095" thickness. (This I infer from the fact that a round with a seated bullet mics about .262", and the bullet mics .243".)

The diameter of the neck of a fired case is about .269".

Up until now, all my loads have used the .260" Wilson bushing, and so I have assumed that this means .002" neck tension.

I've just changed the Wilson bushing to the one marked .259" and have sized the cases with it. Measuring the sized portion of the neck (about the last .18" of the neck) gives .258", and so this is about .001" tighter than I thought I was getting with the Wilson .259" bushing.

So far, I have varied seating depth from .0175" off the lands to .011" ITL. Accuracy was better with bullets seated into the lands. I have varied powder charges of H322 from 26.0 gr. up to 27.5 gr. and of VV133 from 26.5 gr. up to 28.7 gr. In general, I'd say that the VV133 has been slightly better than the H322, and the heavier charge weights have produced the better groups. Of the two bullets tested, I'd say the Bart's have been very slightly better than the Watsons.

So that's where things stood when I began to think about altering neck tension. I thought I'd go with the best seating depth and best charge weight of VV133 and increase the neck tension by .001". I've resized the cases now with the slightly-tighter bushing. Perhaps I should have waited to get your opinions before doing this, but the die is now cast, and only another day at the range will reveal any effects of doing this. One thing I might add: I had read on this forum that some seemed to think that VV133 liked tighter neck tension, and so this was one factor in my decision to go to the .259" bushing.

I'm trying to keep my aspirations realistic with this rifle. It is a lightweight sporter--about 6lbs., 6 oz. bare, with a barrel that mics .595" at the muzzle. I think my optics are fine--a Leupold 6.5-20X40 mm. boosted by Premier Reticles many years ago to 14.5-35. I'm hoping to find a load that will yield an average (over 5-10 consecutive groups) 5-shot group of .50" at 100 yards. This will mean some groups in the .3s (I've shot one group of .34"), but some in the .6s or worse as well. I'm not there yet. The prospect of bringing in another powder, and possibly other bullets, to add to all the variables already in place, is daunting....

 

[Tim Singleton]

If you are not shooting over wind flags groups in the .3s will be hard to luckily come by
The reason some Br shooters use more neck tension is to get deeper into the lands without sticking the bullet. N133 likes a lot of pressure
I would find a nice medium load of 133 say 29.6 gr and work a seating depth to it
That will shoot most days. Some days it just won't and you need 28gr of h322 those days

 

[Richard Coody]

Many thanks to all of you who have chipped in with valuable insights. Just to answer some questions, I don't know the chamber neck diameter (I haven't made a chamber cast), but I suspect it is in the .270"-.272" range. This is the typical Sako 6 PPC-USA chamber, so nothing like the earlier custom .262" chambers.

Yes, I am neck-turning, and have turned the necks to about .0095" thickness. (This I infer from the fact that a round with a seated bullet mics about .262", and the bullet mics .243".)

The diameter of the neck of a fired case is about .269".

Up until now, all my loads have used the .260" Wilson bushing, and so I have assumed that this means .002" neck tension.

I've just changed the Wilson bushing to the one marked .259" and have sized the cases with it. Measuring the sized portion of the neck (about the last .18" of the neck) gives .258", and so this is about .001" tighter than I thought I was getting with the Wilson .259" bushing.

So far, I have varied seating depth from .0175" off the lands to .011" ITL. Accuracy was better with bullets seated into the lands. I have varied powder charges of H322 from 26.0 gr. up to 27.5 gr. and of VV133 from 26.5 gr. up to 28.7 gr. In general, I'd say that the VV133 has been slightly better than the H322, and the heavier charge weights have produced the better groups. Of the two bullets tested, I'd say the Bart's have been very slightly better than the Watsons.

So that's where things stood when I began to think about altering neck tension. I thought I'd go with the best seating depth and best charge weight of VV133 and increase the neck tension by .001". I've resized the cases now with the slightly-tighter bushing. Perhaps I should have waited to get your opinions before doing this, but the die is now cast, and only another day at the range will reveal any effects of doing this. One thing I might add: I had read on this forum that some seemed to think that VV133 liked tighter neck tension, and so this was one factor in my decision to go to the .259" bushing.

I'm trying to keep my aspirations realistic with this rifle. It is a lightweight sporter--about 6lbs., 6 oz. bare, with a barrel that mics .595" at the muzzle. I think my optics are fine--a Leupold 6.5-20X40 mm. boosted by Premier Reticles many years ago to 14.5-35. I'm hoping to find a load that will yield an average (over 5-10 consecutive groups) 5-shot group of .50" at 100 yards. This will mean some groups in the .3s (I've shot one group of .34"), but some in the .6s or worse as well. I'm not there yet. The prospect of bringing in another powder, and possibly other bullets, to add to all the variables already in place, is daunting....

the 6ppc is an inherently accurate round. i see no reason that your rifle shouldn't shoot in the 1's and 2's with a little work. you may see that fade some after that barrel heats up.

kind of what i expected. on your next batch of brass i would.not turn the necks so much. you really only want about .003 clearance between loaded round and chamber. you far exceed that. thicker necks will give you more neck tension with a larger bushing.

6ppc likes them jammed and hot.

now what is the barrel twist. those 60 grain bullets like 13.5 twist. for heavier you want a 12 or faster